Dielectric layer for gallium nitride transistor

Abstract

A dielectric layer for a gallium nitride transistor is disclosed. In one example, the dielectric layer has a hydrogen content of less than or equal to 10% by atomic percentage. In one example, both a dielectric layer formed before a conductive electrode of the transistor and a dielectric layer formed after the conductive elective electrode have a hydrogen content of less than or equal to 10% by atomic percentage. In one example, the dielectric layer formed before the conductive electrode is formed by a LPCVD process and the dielectric layer formed after the conductive electrode is formed by a sputtering process.

1 . A method for forming a gallium nitride transistor comprising:
 forming a first dielectric layer over a gallium nitride material, the first dielectric layer having a hydrogen content of less than or equal to 10% by atomic percentage;   forming a conductive electrode structure of the gallium nitride transistor over the gallium nitride material after the forming the first dielectric layer, the gallium nitride transistor including a structure in the gallium nitride material;   forming a second dielectric layer after the forming the conductive electrode structure, the second dielectric layer having a hydrogen content of less than or equal to 10% by atomic percentage.   
     
     
         2 . The method of  claim 1 , wherein forming the first dielectric layer includes forming the first dielectric layer to include silicon nitride by a low pressure chemical vapor deposition (LPCVD) process with a minimum chamber deposition temperature of at least 650 C. 
     
     
         3 . The method of  claim 1 , wherein:
 the first dielectric layer has a hydrogen content of less than or equal to 5% by atomic percentage;   the second dielectric layer has a hydrogen content of less than or equal to 5% by atomic percentage.   
     
     
         4 . The method of  claim 1 , wherein forming the first dielectric layer includes forming the first dielectric layer to include silicon nitride by a low pressure chemical vapor deposition (LPCVD) process with a maximum chamber deposition pressure of 500 mTorr or less. 
     
     
         5 . The method of  claim 1 , wherein forming the second dielectric layer includes forming the second dielectric layer by a sputtering process. 
     
     
         6 . The method of  claim 5  wherein the second dielectric layer includes silicon nitride. 
     
     
         7 . The method of  claim 6  wherein forming the second dielectric layer includes forming the second dielectric layer by a sputtering process in a poisoned mode. 
     
     
         8 . The method of  claim 5  wherein the forming the second dielectric layer includes sputtering silicon nitride in the presence of a nitrogen bearing gas and an argon bearing gas wherein the mass ratio of nitrogen to argon is at least 0.5. 
     
     
         9 . The method of  claim 1  further comprising:
 forming a third dielectric layer over the second dielectric layer, wherein the third dielectric layer has a hydrogen content less than or equal to 10% by atomic percentage. 
 
     
     
         10 . The method of  claim 1  further comprising:
 forming a drain electrode over the gallium nitride material; 
 forming a source electrode over the gallium nitride material; 
 forming a first opening in the second dielectric layer for forming a first electrically conductive structure to be electrically coupled to the drain electrode; 
 forming a second opening in the second dielectric layer for forming a second electrically conductive structure to be electrically coupled to the source electrode; 
 wherein the conductive electrode structure is a gate electrode structure. 
 
     
     
         11 . The method of  claim 1  further comprising:
 forming a semiconductor layer over the gallium nitride material, the semiconductor layer having a band gap different than that of the gallium nitride material, wherein the first dielectric layer is formed over the semiconductor layer. 
 
     
     
         12 . The method of  claim 1  further comprising:
 after forming the first dielectric layer, patterning the first dielectric layer and the gallium nitride material to form a mesa; 
 forming a third dielectric layer over the first dielectric layer, wherein the third dielectric layer is formed on sidewalls of the mesa, the third dielectric layer having a hydrogen content of less than or equal to 10% by atomic percentage; 
 wherein the conductive electrode is formed after the forming the third dielectric layer. 
 
     
     
         13 . The method of  claim 1  wherein the first dielectric layer and the second dielectric layer each have a buffered oxide wet etch rate in a 6:1 buffered oxide etchant of 2 A per second or less. 
     
     
         14 . The method of  claim 1  wherein the first dielectric layer and the second dielectric layer each have a dielectric breakdown strength of 0.5 Mega Volts/cm or greater. 
     
     
         15 . A method for forming a gallium nitride transistor comprising:
 forming by a low pressure chemical vapor deposition process a first dielectric layer over a gallium nitride material, wherein a minimum deposition temperature of the low pressure chemical vapor deposition process is 650 C or greater;   forming a conductive electrode structure of the gallium nitride transistor over the gallium nitride material after the forming the first dielectric layer, the gallium nitride transistor including a structure in the gallium nitride material;   forming a second dielectric layer by a sputtering process after forming the conductive electrode structure;   wherein the first dielectric layer and the second dielectric layer each have a hydrogen content by atomic percentage of less than or equal to 10%.   
     
     
         16 . The method of  claim 15  wherein the forming the second dielectric layer includes sputtering silicon nitride in the presence of a nitrogen bearing gas and an argon bearing gas wherein the mass ratio of nitrogen to argon is at least 0.5. 
     
     
         17 . The method of  claim 15  wherein the first dielectric layer and the second dielectric layer each have a wet etch rate in a 6:1 buffered oxide etchant of 2 A per second or less. 
     
     
         18 . The method of  claim 15  wherein the sputtering process is performed in a poisoned mode. 
     
     
         19 . (canceled) 
     
     
         20 . A method for forming a gallium nitride transistor comprising:
 forming a first dielectric layer including silicon nitride over a gallium nitride material, the first dielectric layer having a hydrogen content of less than or equal to 10% by atomic percentage;   forming a gate conductive electrode structure of the gallium nitride transistor over the gallium nitride material after the forming the first dielectric layer, the gallium nitride transistor including a structure in the gallium nitride material;   forming a source conductive electrode structure of the gallium nitride transistor over the gallium nitride material after the forming the first dielectric layer;   forming a drain conductive electrode structure of the gallium nitride transistor over the gallium nitride material after the forming the first dielectric layer;   forming a second dielectric layer after the forming the gate conductive electrode structure, the source conductive electrode structure, and the drain conductive electrode structure, the second dielectric layer having a hydrogen content of less than or equal to 10% by atomic percentage;   forming a third dielectric layer after the forming the second dielectric layer, the third dielectric layer having a hydrogen content of less than or equal to 10% by atomic percentage.   
     
     
         21 . The method of  claim 1  wherein the first dielectric layer includes silicon nitride and the second dielectric layer includes silicon nitride.